1. Field of Invention
The present invention relates largely to medical devices concerning the brain, and is a method and apparatus to non-invasively localize, in three dimensions (3D), electrical activity in the cerebral cortex of the brain, display the localized electrical activity in the form of 3D “motion pictures”, and to perform statistical analysis and quantification of the localized electrical activity, all in near-real time.
2. Prior Art
The human cerebral cortex is the convoluted outer surface of the brain, commonly known as ‘gray matter’ and is responsible for many of the higher functions including those associated with thought, action, emotion and sensation. The cerebral cortex, largely due to its complexity, is also susceptible to a large number of disorders and diseases, many of which lack proper objective diagnoses, or require expensive medical equipment to properly diagnose.
Often, elucidating specific cortical functions or diagnosing diseases requires the three-dimensional (3D) localization of what regions of the cerebral cortex are responsible, and subsequent display of these regions in the form of one or more images. There are a number of existing technologies that have been utilized that accomplish this, including examples such as:                a. Magnetic Resonance Imaging (MRI) and Functional Magnetic Resonance Imaging (fMRI); U.S. Pat. No. 4,812,720 (1989)        b. Positron Emission Tomography (PET); U.S. Pat. No. 4,284,890 (1981)        c. Single Photon Emission Computed Tomography (SPECT); U.S. Pat. No. 4,584,478 (1986)        d. X-Ray Computed Tomography (CT); U.S. Pat. No. 3,922,552 (1975)        e. Magnetoencephalography (MEG); U.S. Pat. No. 4,591,787 (1986)        
Each of these technologies has its strengths and weaknesses. Some of the technologies listed above are capable of localizing specific features to a resolution of less than 1 mm, although only MEG is capable of capturing many three-dimensional images per second at that resolution; the others require seconds to minutes for each image. MEG is also the most costly of the above technologies and the least accessible. In general, these technologies are very expensive, typically $1,000,000-$10,000,000 USD per machine. In addition to the cost of the machine itself, technical staff, maintenance fees, specialized environments, and chemical or radioactive agents may also be required. For example, SPECT and PET scanners perform their function by detecting injected radioisotopes to obtain functional and/or spatial information; the sensitivity of MRI scanners can be increased by introducing chemical contrast agents into subjects; and MEG scanners require magnetically shielded rooms, often located underground. These machines are physically large and require entire spaces to be devoted to their function, hence restricted to larger medical institutions and universities, and most definitely not portable. It is primarily for the aforementioned reasons that these technologies are largely inaccessible to both members of the general population and much of the academic and private research community.
Consequently, there is a clear need for new technologies that can perform to a similar level, but for much-reduced base and operating costs, while increasing portability.
There exists, however, a related technology that can match the temporal resolution of MEG, is portable, but cannot localize in three dimensions events that take place within the cerebral cortex. The related technology, the electroencephalograph (EEG) recorder, can measure electrical potentials between any number of electrodes placed on a subject's scalp, and changes in the electrical activity of the cerebral cortex will produce a change in voltage, or electric potential, of the electrode. When the individually measured changes in voltage from an electrode are measured over time, it becomes a signal. The electrical activity of the cerebral cortex is thought to originate from the interactions between the firing (and resulting movement of ions) of excitatory pyramidal cells and inhibitory interneurons.
Attempts have been made within prior art to localize EEG signals and to elucidate the spatiotemporal patterns of electrical activity within the cerebral cortex, although there have been significant shortcomings in the results that these methodologies produce; for example, U.S. Pat. No. 4,407,299 to Culver (1983) restricts localization to a two-dimensional topographic map based on the known positions of the EEG electrodes but does not offer any depth information; U.S. Pat. No. 5,361,774 to Yamazaki requires prior knowledge of the function in question to generate an assumption by which the localization solution can refine; and U.S. Pat. No. 5,701,909 to Amir requires extensive computer processing due to solution-specific optimization which precludes widespread general use. U.S. Pat. No. 5,307,807 to Valdes Sosa (1994) describes a method and system to localize EEG signals in three dimensions, using an inverse solution approximation source localization algorithm, however it does not reduce to practice any applications, nor is it performed in near real-time, significantly reducing the clinical relevance, and it relies on tomographs (2D slices) to convey three-dimensional data, which complicates the interpretation of contiguous 3D data.